Owing to advantages of wireless networks such as convenience in use, low deployment cost and high mobility, various wireless network standards have been developed rapidly in the modern network technologies. Although communication protocols of these wireless network standards vary greatly from each other, most of the wireless network standards have similar service architecture. Specifically, the service architecture of many wireless networks includes a service providing apparatus and a service consuming apparatus, in which network service resources are provided by the service providing apparatus to the service consuming apparatus. For instance, in a Vehicle-to-Roadside communication system of the telematics field, services are provided by a road side unit (RSU) to an on-board unit (OBU). In this kind of service architecture, the service providing apparatus has larger communication coverage while the service consuming apparatus has smaller communication coverage, which characteristic is known as the link asymmetry. The link asymmetry characteristic leads to a number of problems.
Now, the problems of a conventional wireless network caused by the link asymmetry will be explained with reference to a wireless network application scenario illustrated in FIGS. 1A, 1B and 1C. A wireless network 10a illustrated in FIG. 1A comprises a service providing apparatus 11a and a service consuming apparatus 13a. More specifically, in the scenario illustrated in FIG. 1A, communication coverage of the service providing apparatus 11a covers the service consuming apparatus 13a, so signals transmitted by the service providing apparatus 11a can be received by the service consuming apparatus 13a. However, communication coverage 130a of the service consuming apparatus 13a does not cover the service providing apparatus 11a, so a response signal to be transmitted by the service consuming apparatus 13a to the service providing apparatus 11a will fail to be transmitted correctly to the service providing apparatus 11a. Consequently, it is impossible for the service providing apparatus 11a and the service consuming apparatus 13a to perform a handshake process with each other to establish a connection therebetween. This causes repeated transmission of the response signal by the service consuming apparatus 13a, which unnecessarily occupies the network bandwidth. This is the first problem caused by the link asymmetry.
Secondly, referring to FIG. 1B, a wireless network 10b illustrated therein comprises a service providing apparatus 11b, a first service consuming apparatus 13b and a second service consuming apparatus 15b. Particularly, when the first service consuming apparatus 13b and the second service consuming apparatus 15b are not covered by each other's communication coverage 130b, 150b, it means that they cannot confirm each other's presence in the network. Consequently, the first service consuming apparatus 13b and the second service consuming apparatus 15b may send service requests to the service providing apparatus 11b simultaneously without coordinating with each other. This causes the service request signals transmitted to the service providing apparatus 11b to generate serious interference, thereby increasing the loading of the service providing apparatus 11b. This is the second problem caused by the link asymmetry.
Next, the second problem caused by the link asymmetry will be further explained with reference to FIG. 1C. FIG. 1C is a schematic view illustrating a connection period 16 used by the wireless network 10b. The connection period 16 is divided into two kinds of sections, i.e., control channel periods 164, 168 and service channel periods 162, 166. Within the control channel period 164, the service providing apparatus 11b broadcasts service providing signals 180a, 180b. Upon receiving the service providing signals 180a, 180b, the service consuming apparatuses 13b, 15b transmit data within the service channel period 166; more specifically, the service consuming apparatus 13b transmits data 190a, and the service consuming apparatus 15b transmits data 190b. However, the time intervals within which the data 190a, 190b are transmitted are partially overlapped with each other, which leads to the so-called collision.
Referring further to FIG. 1D, a wireless network 10c illustrated therein comprises a service providing apparatus 11c, a first service consuming apparatus 13c and a second service consuming apparatus 15c. The third problem caused by the link asymmetry is that, signals of the second service consuming apparatus 15c will cause communication interference between the first service consuming apparatus 13c and the service consuming apparatus 11c. Specifically, because the second service consuming apparatus 15c is located within communication coverage 110c of the service providing apparatus 11c, the second service consuming apparatus 15c will be able to receive signals transmitted by the service providing apparatus 11c and transmit a response signal accordingly. However, as described above, because the communication coverage 150c of the second service consuming apparatus 15c does not cover the service providing apparatus 11c, the second service consuming apparatus 15c will transmit the response signal continuously. In this case, the second service consuming apparatus 15c will cause interference to the first service consuming apparatus 13c that is currently conducting service transmissions with the service providing apparatus 11c. In other words, because the communication coverage 150c of the second service consuming apparatus 15c also covers the first service consuming apparatus 13c, continuous transmission of the request signal by the second service consuming apparatus 15c when it receives no response from the service providing apparatus 11c will cause communication interference to the first service consuming apparatus 13c. 
Accordingly, there remains a need in the art to provide a solution that can overcome the drawbacks of the prior art so as to make data transmissions between the service providing apparatus and the service consuming apparatus more stable and efficient in various wireless networks.